Assume That the Number of Multiplications of Entries Used to Multiply

Short Answer

assume that the number of multiplications of entries used to multiply a p × q and a q × r matrix is
pqr.
-What is the most efficient way to multiply the matrices $$\mathbf { A } _ { 1 } , \mathbf { A } _ { 2 } , \mathbf { A } _ { 3 } \text { of sizes } 10 \times 50,50 \times 10,10 \times 40 \text { ? }$$